Experiment: Admin PWA

lib/load.php

@@ -118,6 +118,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/navigation-page.php';
 require __DIR__ . '/experiments-page.php';
 require __DIR__ . '/global-styles.php';
+require __DIR__ . '/pwa.php';
 
 require __DIR__ . '/block-supports/generated-classname.php';
 require __DIR__ . '/block-supports/elements.php';

lib/pwa.php

@@ -0,0 +1,67 @@
+<?php
+/**
+ * Progressive Web App
+ *
+ * @package gutenberg
+ */
+
+add_filter(
+	'admin_head',
+	function() {
+		$icon_sizes = array( 32, 180, 192, 270, 512 );
+
+		// Ideally we have the WordPress logo as the default app logo in the sizes
+		// below.
+		$icons = array();
+
+		if ( has_site_icon() ) {
+			$type = wp_check_filetype( get_site_icon_url() );
+
+			foreach ( $icon_sizes as $size ) {
+				$icons[] = array(
+					'src'   => get_site_icon_url( $size ),
+					'sizes' => $size . 'x' . $size,
+					'type'  => $type['type'],
+				);
+			}
+		}
+
+		$manifest = wp_json_encode(
+			array(
+				'name'        => get_bloginfo( 'name' ),
+				'icons'       => $icons,
+				'display'     => 'standalone',
+				'orientation' => 'portrait',
+				'start_url'   => admin_url(),
+				// Open front-end, login page, and any external URLs in a browser modal.
+				'scope'       => admin_url(),
+			)
+		);
+
+		// Must be at the admin root so the scope is correct. Move to the
+		// wp-admin folder when merging with core.
+		$service_worker_url = admin_url( '?service-worker' );
+
+		echo '<link rel="manifest" href=\'data:application/manifest+json,' . $manifest . '\'>';
+		echo '<script>
+			if( "serviceWorker" in window.navigator ) {
+				window.addEventListener( "load", function() {
+					window.navigator.serviceWorker.register( "' . $service_worker_url . '" );
+				} );
+			}
+		</script>';
+	}
+);
+
+add_filter(
+	'load-index.php',
+	function() {
+		if ( ! isset( $_GET['service-worker'] ) ) {
+			return;
+		}
+
+		header( 'Content-Type: text/javascript' );
+		echo file_get_contents( __DIR__ . '/service-worker.js' );
+		exit;
+	}
+);

lib/service-worker.js

@@ -0,0 +1,14 @@
+/* global self */
+
+// https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerGlobalScope/skipWaiting
+self.addEventListener( 'install', function ( event ) {
+	event.waitUntil( self.skipWaiting() );
+} );
+
+// https://developer.mozilla.org/en-US/docs/Web/API/Clients/claim
+self.addEventListener( 'activate', function ( event ) {
+	event.waitUntil( self.clients.claim() );
+} );
+
+// Necessary for Chrome to show the install button.
+self.addEventListener( 'fetch', function () {} );